Server and Method for Managing Domain Names in a Network

ABSTRACT

A domain name server includes a zone file containing partitioning rules that define the partitioning of all subfolders of this domain into subzones. The DNS data of each of these subzones is hosted by a partition server that is able to obtain from the zone file information for identifying the partition server able to respond to a query sent by a client to obtain a DNS folder.

BACKGROUND OF THE INVENTION

The present invention relates to the general field of domain nameservers in a telecommunications network. The Domain Name System (DNS)architecture defined by the Internet Engineering Task Force (IETF)Request For Comments (RFC) 1034 manages domain names in a network.

This architecture introduces the domain concept to designate a group ofmachines on the network.

FIG. 1 represents an architecture of this kind. The domains .,.fr,.com,ft.com, and rd.ft.com contain subdomains.

For example, the domain ft.com includes three subdomains www.ft.com,rd.ft.com, and user.ft.com.

The domains that are underlined in FIG. 1 are known as terminal domains.A terminal domain:

-   -   can represent one or more physical machines, like the terminal        domain www.rd.ft.com, for example;    -   but can also not represent any physical machine, like the        terminal domain user.ft.com, for example, which here consists of        personal information of the person specified by “user”.

A domain that includes one or more subdomains is associated with adomain server, also referred to as a name server.

The domain server includes a zone file.

The domains are logically linked, so that DNS data of any domain can beobtained by interrogating the name servers progressively, starting withthe root server.

In the present document, the term information refers in particular tothe IP (Internet Protocol) address of a domain, a text zone, or anyfield (CNAME, etc.) associated with a domain.

With the growing popularity of the Internet, domain name servers areincreasingly difficult to administer.

In particular, update operations, which are additional to thetraditional reading operations (directory function), considerablyincrease the number of transactions managed by these servers. Moreover,these transactions require operations to synchronize master and slaveservers and also consume network resources.

Also, domain name servers host increasingly large amounts of data andincreasingly large zones.

Previously, domain names contained hardly more information than IPaddresses, not exceeding around twenty bytes. Nowadays, the DNS hostsmuch larger profiles (approximately 200 bytes), for example ENUMservices (as described in IETF RFC 2916).

One known solution to this problem is to create subdomains, the nameservers of the subdomains created in this way hosting some of the datapreviously hosted by the domain from which they originate.

That solution adds another level to the domain hierarchy, however, whichcomplicates the new subdomain name.

This complexity of the subdomain name can be perceived as a drawback,especially if the name of the subdomain is used for commercial oradvertising purposes.

OBJECT OF THE INVENTION

The invention aims to address the above problem.

To this end, a first aspect of the invention proposes a domain server ina telecommunications network, adapted to manage DNS queries relating tothe domain, including means for receiving from a client device a queryseeking to obtain DNS data of that domain. The server includes:

-   -   a zone file containing a partitioning rule defining a        partitioning of the set of subdomains of the domain into        subzones, the DNS data of each of the subzones being hosted by a        partition server;    -   means for obtaining from the zone file sufficient information to        identify the appropriate partition server capable of responding        to the query; and    -   mean for sending the useful information to the client device in        response to the query.

The term “zone” is generally used to refer to data hosted by a serverand the term “domain” to designate the logical entity. However, theterms “zone” and “domain” are often used interchangeably in theliterature.

In the remainder of this document, in the context of the invention, thepartition servers are child servers of the domain name server, alsoknown as the parent server.

Thus the invention hosts the data of a domain in child servers thatdefines the partitioning of the subdomains of that domain.

The parent server can retain some of the data of its domain, of course.

The person skilled in the art will understand that it is not a questionof the same zone being managed in its entirety by a number of servers,which is already provided for by the DNS, but rather of fragmenting adomain into small zones that are more easily administered by the domainname servers.

In particular, the invention dissociates the logic for managing the dataof a domain from its use, which is highly advantageous.

The core of the invention resides more precisely in the zone file readby the server. Thus a second aspect of the invention is directed to adata structure consisting of a computer file that can be read by adomain server in a telecommunications network and includes:

-   -   lines defining a rule for partitioning the set of subdomains of        the domain into subzones; and    -   lines including identifiers of partition servers each hosting        the DNS data of one of said subzones.

In practice, the administrator of a zone defines the logicalpartitioning of a domain, which amounts to dividing the subdomains ofthat domain into different groups, each group being hosted either by achild server or by the parent server itself.

The computer file of the invention contains mainly a list of partitionserver identifiers (i.e. child servers and where appropriate parentserver) and a partitioning rule used to identify a particular partitionserver adapted to supply the required DNS data.

The useful information sent back by the server for redirecting itsclient can be of various types.

For example, it can include one or more of the following:

-   -   the partitioning rule(s) accompanied by the names or aliases of        the partition servers;    -   the name of the appropriate partition server; and    -   an alias of the appropriate partition server.

If the useful information consists of the partitioning rule, either theclient device or its administrator must interpret the partitioning ruleto determine the name of the partition server.

A third aspect of the invention is directed to a client data processingsystem of a domain name server in a telecommunications network,including means for sending said server a query seeking to obtain DNSdata of that domain. This client data processing system includes meansfor interpreting a regular expression received in response to the query,this interpretation enabling it to obtain the name of a partition servercapable of responding to the query.

Once it knows the name or alias of the partition server, the clientdevice can interrogate that server to obtain the required data,proceeding step by step as is usual in the DNS architecture.

The useful information preferably further includes the address of thepartition server, associated with one or more of the above elements.

In a preferred embodiment, the partitioning rule for identifying thepartition server is a regular expression and the domain name serverincludes means for interpreting that regular expression to obtain theaddress of the partition server and send it to the client device.

A regular expression can be defined as a line of computer code definingthe search for a pattern within a character string.

This particularly advantageous feature greatly facilitates the task ofusers having no client device of the invention adapted to interpretregular expressions.

In a correlated way, the invention relates to a method of managing DNSqueries relating to a domain in a telecommunications network, includinga step of receiving from a client device a query seeking to obtain DNSdata of that domain.

The method includes:

-   -   a step of reading a zone file including a partitioning rule        defining partitioning of the set of the subdomains of the domain        into subzones, the DNS data of each of the subzones being hosted        by a partition server;    -   a step of obtaining from the zone file sufficient information to        identify the partition server capable of responding to said        query; and    -   a step of sending said useful information to the client device        in response to the query.

The invention is also directed to a method of obtaining DNS data of adomain in a telecommunications network, including a step of sending aquery aiming to obtain the data.

This method includes a step of interpreting a regular expressionreceived in response to the query and obtaining from that interpretationthe name of a partition server capable of responding to the query.

The steps of the management method and the method of obtaining data arepreferably determined by computer program instructions.

Consequently, the invention is also directed to a computer program on aninformation medium, adapted to be executed in a computer, a domain nameserver or a client device, and including instructions adapted to executea domain name management method or a method of obtaining data asoutlined above.

These programs can use any programming language and take the form ofsource code, object code or an intermediate code between source code andobject code, such as a partially-compiled form, or any other desirableform.

The invention is also directed to a computer-readable information mediumthat can also be read by a domain name server and contains instructionsof a computer program as referred to above.

The information medium can be any entity or device capable of storingthe program. For example, the support can include storage means, such asa ROM, for example a CD ROM or a microelectronic circuit ROM, ormagnetic storage means, for example a diskette (floppy disk) or a harddisk.

Moreover, the information medium can be a transmissible medium such asan electrical or optical signal, which can be routed via an electricalor optical cable, by radio or other means. The program of the inventioncan in particular be downloaded over an Internet-type network.

Alternatively, the information medium can be an integrated circuit intowhich the program is incorporated, the circuit being adapted to executethe method in question or to be used in its execution.

BRIEF DESCRIPTION OF THE DRAWINGS

Other features and advantages of the present invention emerge from thedescription given below with reference to the appendices and drawings,which show one non-limiting embodiment of the invention and in which:

Appendices 1 and 2 represent the principal lines of a zone file of aparent domain name server in two embodiments of the invention;

Appendix 3 represents the principal lines of a zone file of a childdomain name server of a preferred embodiment the invention;

FIG. 1, already described, represents an example of a DNS domain treeknown to the person skilled in the art;

FIG. 2 represents a telecommunications network including a parent domainname server of the invention and two partition servers;

FIG. 3 is a flowchart representing the principal steps of a preferreddomain name management method of the invention; and

FIG. 4 is a flowchart representing the principal steps of a preferredmethod of the invention for obtaining data.

DETAILED DESCRIPTION OF AN EMBODIMENT OF THE INVENTION

FIG. 2 represents a telecommunications network 1 and a domain nameserver ns1 managing a domain (or zone) z1.com.

As mentioned above, to implement the invention, this zone z1.com isdivided into subzones. A partitioning rule is used for this, which inthe present example distributes the names of the subdomains of thedomain z1.com as follows:

-   -   subdomain names in which the first letter is from a to m are        hosted by the child server ns1-part1; and    -   subdomain names in which the first letter is from n to z are        hosted by the child server ns1-part2.

Accordingly, when a client CL1 interrogates the parent server ns1 toobtain DNS data relating to the subdomain domain2.z1.com, the clientreceives, in response to this query, useful information that redirectsit to the partition server ns1-part1, since the first letter of the nameof this subdomain (domain2.z1.com) is the letter d, which lies betweenthe letters a and m.

For the client CL1 and for each of the domain name servers ns1,ns1-part1, and ns1-part2, FIG. 2 shows means 10 for receiving andsending data over the telecommunications network 1, consisting forexample of a network card associated with drivers managing the HyperTextTransfer Protocol (HTTP) and conventional computer processor means 20,namely a processor, a memory containing computer programs, and a randomaccess memory for temporarily storing variables needed to execute theprograms.

The processor means 20 of the server ns1 are adapted to execute theinstructions of a computer program implementing the principal steps E10to E50 of the management method of the invention shown in FIG. 3.

Similarly, the processor means 20 of the client device CL1 are adaptedto execute the instructions of a computer program implementing theprincipal steps F10 to F30 of the method of the invention for obtainingDNS data shown in FIG. 4.

It is assumed that, using the communication means 10, the client CL1sends (step F10 in FIG. 4) a query to the domain name server ns1 at IPaddress 10.193.161.50 to obtain the IP address of the subdomaindomain2.z1.com, also denoted IP(domain2.z1.com).

This query can be of the following type, for example:

-   -   DIG 10.193.161.50 +norecurse domain2.z1.com, DIG (Domain        Information Groper) being a tool known to the person skilled in        the art for interrogating domain name servers in the DNS        architecture.

The receiver means 10 of the domain name server ns1 receive this queryin the step E10 in FIG. 3.

The person skilled in the art will realize that, the DIG commandcontaining no type, the data that the client is looking for is data oftype A, namely the IP address of the domain2.z1.com.

Following the step E10 of receiving the query from the client CL1, thename processor means 20 of the server ns1 read in a step E20 the zonefile FZ1.zone defining the management of the zone z1.com by that serverns1.

This zone file FZ1.zone can be stored in a memory 30 of the server ns1,for example. It can also be stored in another machine.

Appendix 1 shows the principal lines of this zone file FZ1.zone.

Lines conforming to the DNS standard and known to the person skilled inthe art are not described here.

This file includes lines L9 and L10 including the identifiers ns1-part1and ns1-part2 of the partition servers that manage the DNS data of thezone z1.com.

The person skilled in the art will realize that, in line L9, the addressof the server ns1-part1.z1.com on the network 1 is 10.193.161.73 (fieldA) and that server 1 is an alias (field CNAME) of the partition serverns1-part2.z1.com, the address of that partition server on the network 1being 10.193.161.30, as indicated in line L11.

Moreover, lines L6 and L7 of the zone file FZ1.zone include apartitioning rule for redirecting the client CL1, in this example:

-   -   to the server ns1-part1.z1.com for any query to obtain data        associated with a subdomain whose first letter is from a to m;        and    -   to the server ns1-part2.z1.com for the others.

To be more precise, the field “regexp” contains a regular expression forwhich the query sent by the client must be substituted. This resulttherefore constitutes the next query to be sent by the client.

According to the invention, the regular expression consists of a testused afterwards to indicate the name of the server that is hosting therequired data.

Appendix 2 shows the principal lines of a zone file FZ1 a.zone of theserver ns1 of a second embodiment of the invention.

Only lines L6 and L7 differ from the zone file FZ1.zone of Appendix 1.

This zone file differs from the previous one in that the redirectionindication is placed in the field “regexp”, the replacement field beingempty.

Alternatively, it could also be decided to specify a new service, toprevent any interpretation of the nature of the partitioning rule (here“service” refers to the logic that the client must adopt in order toresolve the query correctly). Accordingly, by choosing Domain to NameServer (D2NS) acronym, the Naming Authority Pointer (NAPTR) would be asfollows:

class type flags service regexp replacement ns1 IN NAPTR “a” “D2NS”“!{circumflex over ( )}[a-m] !ns1-part1.z1.com.!”

The “service” field is defined in RFC 3403. It is a character stringthat enables the client to identify the processing it must carry out. Inthis variant, the service D2NS is introduced in order to advise theclient how the fields of the rule set out in the NAPTR field must beinterpreted.

Alternatively, it could equally be decided to specify the name of thepartitioning rule as an argument of the function of the service, inorder to prevent any interpretation of the nature of the partitioningrule. Thus by choosing Domain to Name Server (D2NS) acronym, the fieldNAPTR would be as follows:

class type flags service regexp replacement IN NAPTR “a” “D2NS!ns1!”“!{circumflex over ( )}[a-m] !ns1-part1.z1.com.!”

Alternatively, it could equally be decided to specify the name of thepartitioning rule in the field “regexp”, to prevent any interpretationof the nature of the partitioning rule. Thus by choosing Domain to NameServer (D2NS) acronym, the NAPTR field would be as follows, for example:

class type flags service regexp replacement IN NAPTR “a” “D2NS!ns1!”“!{circumflex over ( )}[a-m] !\\:ns1-part1.z1.com.!”

The benefit of not giving the rule name as the domain name is that thisguarantees that all the rules will be at the root of the zone andprevents incorrect interpretation of the domain name relating to therule.

It is therefore preferable for the client to be able to determinewhether the name to which the NS-type field refers is a domain name or apartitioning rule.

The benefit of showing the rule as a domain name is that this specifiesthe name of the domain for the next interrogation. Conventionally, thenext interrogation relates to the field with the type A. In theinvention, this interrogation relates to the NAPTR type field.

In the standard DNS, the field ns of the server managing the partitionspoints to a domain name that a query relating to a field of type A mustuse. This no longer applies to zone files of the invention.

In the preferred embodiment of the invention described here, the fieldns refers to an NAPTR type field containing the partitioning rules (L6and L7).

Of course, creating a new type of field could be envisaged instead ofusing the NAPTR field as described for this embodiment of the invention.

The fact that the field ns associated with the domain name z1.com doesnot point to a type A field is characteristic of a zone file of theinvention.

The presence of partitioning rules is another.

In one preferred embodiment of the invention, the processor means 10 ofthe server ns1 are adapted to interpret (step E30) the regularexpressions of lines L6 and L7 to obtain from the domain namedomain2.z1.com the name ns1-part1 of the distribution server hosting therequired DNS data.

Be this as it may, according to the invention, the processor means 10 ofthe server ns1 are adapted to obtain, in a step E40, useful informationfor redirecting the client CL1 to the partition server ns1-part1.

This useful information can be of various types.

For example, it can include the partitioning rule L6, L7.

The useful information obtained by the server ns1 can also include thename of the partition server (ns1-part1.z1.com).

It can further include an alias of the server. Accordingly, assumingthat the client CL1 interrogates the server ns1 using a domain namebeginning with the letter “r”, the alias server1 can form part of theuseful information for redirecting the client CL1 to the partitionserver hosting the data of this domain, namely ns1-part2.z1.com here.

In one preferred embodiment of the invention, the useful information forredirection also includes the IP address 10.193.161.30 of a partitionserver associated with one or more of the following: the partitioningrule L6, L7, the name ns1-part2 of the partition server or the aliasserver1 of that server.

Returning to FIG. 3, the name server ns1 sends a response including theuseful information obtained in the steps E30 and E40 to the client CL1in a step E50.

The client CL1 receives this response in a step F20 represented in FIG.4.

To be more precise, the response to the query DIG mentioned above cantake one of the following forms:

; <<>> DiG 9.3.1 <<>> domain.z1.com ;; global options: printcmd ;; Gotanswer: ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 21511 ;;flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 4, ADDITIONAL: 4 ;;QUESTION SECTION: ;domain.z1.com. IN A ;; ANSWER SECTION: domain.z1.com. 300 IN A 212.78.202.252 ;; AUTHORITY SECTION: z1.com. 80394 IN NS ns1;; ADDITIONAL SECTION: Class type order pref flags service regexpreplacement ns1 IN NAPTR 100 50 “a” “ ” “!{circumflex over ( )}[a-m]”ns1-part1.z1.com ns1 IN NAPTR 100 50 “a” “ ” “!{circumflex over( )}[n-z]” ns1-part2.z1.com ns1-part1.z1.com. IN A 10.193.161.73ns1-part2.z1.com. IN CNAME  server1 server1 IN A 10.193.161.30 ;; Querytime: 91 msec ;; SERVER: 10.193.117.254#53(10.193.117.254) ;; WHEN: FriApr 22 16:14:46 2005 ;; MSG SIZE rcvd: 217

According to the invention, the processor means 20 of the client deviceCL1 are adapted to interpret the partitioning rule L6, L7 contained inthe response, if necessary.

Here, the client device CL1 determines from this interpretation that thename of the partition server containing the required data is ns1-part1.

Be this as it may, the useful information for redirection contained inthe response is processed by the client CL1 which recognizes that itmust interrogate the server ns1-part1.z1.com to obtain the IP address ofthe domain domain2.z1.com.

To this end it sends (step F10) a query that is received in a step E10by the communication means 20 of the child server ns1-part1.

The zone file FZ1-part1.zone that manages the partition of the serverns-part1 is set out in Appendix 3.

On reception of this query, the child server ns-part 1 reads (step E20)the zone file FZ1-part1.zone and obtains (step E40) the address10.193.161.33 of the domain domain2.z1.com (see line L.13 of Appendix3).

This address is sent to the client CL1 in the step E50.

In the embodiment of the invention described here, the zone fileFZ1.part1.zone of the child server ns1-part1 also includes informationfor redirecting the client CL1 if its has interrogated the serverns1-part1 by mistake, for example to obtain data associated with asubdomain name beginning, for example, with the letter t.

In that case, the child server ns-part1 sends information enabling theclient CL1 to interrogate the right server, namely ns1-part2.

In this case the response of the server ns1-part1 is preferably in theform:

z1.com.   IN  ns  ns1 Class type order pref flags service regexpReplacement ns1 IN NAPTR 100 50 “a” “D2NS” “!{circumflex over ( )}[a-m]”ns1-part1.z1.com. ns1 IN NAPTR 100 50 “a” “D2NS” “!{circumflex over( )}[n-z]” ns1-part2.z1.com. ns1-part1.z1.com.  IN  A   10.193.161.73ns1-part2.z1.com.  IN  A   10.193.161.30

Note that this is an abnormal situation, as the client has acquired thepartitioning rule before interrogating the partition server, because therule has been communicated to it.

APPENDIX 1 FZ1.zone $TTL 86400 //L1 z1.com. IN SOAlocalhost.root.localhost { } //L2 z1.com. IN ns ns1 //L3 z1.com IN nsns0 //L4 class type order pref flags service regexp replacement //L5 ns1IN NAPTR 100 50 “a” “ ” “!{circumflex over ( )}[a-m]” ns1-part1.z1.com//L6 ns1 IN NAPTR 100 50 “a” “ ” “!{circumflex over ( )}[n-z]”ns1-part2.z1.com //L7 ns1-part1.z1.com. IN A 10.193.161.73 //L9ns1-part2.z1.com. IN CNAME  server1 //L10 server1 IN A 10.193.161.30//L11 ns0 IN A 10.193.161.30 //L12

APPENDIX 2 FZ1a.zone $TTL 86400 //L1 z1.com. IN SOAlocalhost.root.localhost { } //L2 z1.com. IN ns ns1 //L3 z1.com IN nsns0 //L4 class type order pref flags service regexp Replacement //L5 ns1IN NAPTR 100 50 “a” “D2NS” “!{circumflex over ( )}[a-m]!ns1-part1.z1.com.!” //L6 ns1 IN NAPTR 100 50 “a” “ ” “!{circumflex over( )}[n-z] !ns1-part2.z1.com.!” //L7 ns1-part1.z1.com. IN A 10.193.161.73//L9 ns1-part2.z1.com. IN CNAME  server1 //L10 server1 IN A10.193.161.30 //L11 ns0 IN A 10.193.161.30 //L12

APPENDIX 3 FZ1-part1.zone $TTL 86400 //L1 z1.com. IN SOAlocalhost.root.localhost { //L2 } //L3 z1.com. IN ns ns1 //L4 class typeorder pref flags service regexp Replacement //L5 ns1 IN NAPTR 100 50 “a”“D2NS” “!{circumflex over ( )}[a-m]” ns1-part1.z1.com //L6 ns1 IN NAPTR100 50 “a” “D2NS” “!{circumflex over ( )}[n-z]” ns1-part2.z1.com //L7ns1-part1.z1.com IN A 10.193.161.73 //L9 ns1-part2.z1.com IN A10.193.161.30 //L10 $ORIGIN z1.com domain1 IN A 10.193.161.31 //L12domain2 IN A 10.193.161.33 //L13

1. A server (ns1) of a domain (z1.com) in a telecommunications network(1) adapted to manage DNS queries relating to said domain (z1.com),including means (10) for receiving from a client device (CL1) a queryseeking to obtain DNS data (IP(domain2.z1.com)) of that domain, whereinsaid server comprises: a zone file containing a partitioning ruledefining a partitioning of the set of subdomains (domain1.z1.com,domain2.z1.com) of said domain (z1.com) into subzones, the DNS data ofeach of said subzones being hosted by a partition server; means (10) forobtaining from said zone file sufficient information to identify theappropriate partition server capable of responding to said query; andmean (10) for sending said useful information to the client device (CL1)in response to said query.
 2. A server according to claim 1, whereinsaid useful information includes at least one of the following: saidpartitioning rule (L6, L7) accompanied by the names (ns1-part1,ns1-part2) or aliases (server1, server2) of said partition servers; thename (ns1-part2) of said appropriate partition server; and an alias(server2) of said appropriate partition server.
 3. A server according toclaim 2, wherein said useful information further includes the address(10.193.169.73, 10.193.169.30) of said appropriate partition server. 4.A server according to claim 1, wherein said partitioning rule (L6, L7)is a regular expression for obtaining the address of said appropriatepartition server.
 5. A computer file that can be read by a server (ns1)of a domain (z1.com) in a telecommunications network (1), wherein saidcomputer file comprises: lines (L6, L7) defining a rule for partitioningthe set of the subdomains (domain1.z1.com, domain2.z1.com) of saiddomain (z1.com) into subzones; and lines (L9, L10) including identifiers(ns1-part1, ns1-part2) of partition servers each hosting the DNS data ofone of said subzones.
 6. A method of managing DNS queries relating to adomain (z1.com) in a telecommunications network (1), comprising: a step(E10) of receiving from a client device (CL1) a query seeking to obtainDNS data (IP(domain2.z1.com)) of that domain; a step (E20) of reading azone file (FZ1.zone) including a partitioning rule defining thepartitioning of the set of the subdomains (doman1.z1.com,domain2.z1.com) of said domain (z1.com) into subzones, the DNS data ofeach of said subzones being hosted by a partition server; a step (E30,E40) of obtaining from said zone file (FZ1.zone) sufficient informationto identify said partition server capable of responding to said query;and a step (E50) of sending said useful information to said clientdevice (CL1) in response to said query.
 7. A computer program includinginstructions for executing the steps of the management method accordingto claim 6 when said program is executed by a computer.
 8. Acomputer-readable storage medium storing a computer program includinginstructions for executing the steps of the management method accordingto claim
 6. 9. A data processing system (CL1) client of a server (ns1)of domain names (z1.com) in a telecommunications network (1), includingmeans for sending said server (ns1) a query seeking to obtain DNS data(IP(domain2.z1.com) of that domain, wherein the data processing systemcomprises means (20) for interpreting a regular expression (L6, L7)received in response to said query, this interpretation enabling it toobtain the name of a partition server (ns1-part1) capable of respondingto said query.
 10. A method of obtaining DNS data of a domain (z1.com)in a telecommunications network (1), comprising: a step of sending aquery seeking to obtain said data, and a step of interpreting a regularexpression (L6, L7) received in response to said query and obtainingfrom that interpretation the name of a partition server (ns1-part1)capable of responding to said query.
 11. A computer program includinginstructions for executing the steps of the method according to claim 10of obtaining data when said program is executed by a computer.
 12. Acomputer-readable storage medium storing a computer program includinginstructions for executing the steps of the method according to claim 10of obtaining data.